Resistance of maize to the maize weevil: I. Antibiosis

Abstract

Resistance to damage by maize weevil (Sitophilus zeamais Motsch.) is critically important to subsistence farmers who typically store maize grain on-farm. To evaluate grains antibiosis effects to weevil, 18 inbred lines, six each from Southern Africa, Mexico and CIMMYT-Zimbabwe were mated in sets, according to a North Carolina Design II. Hybrids were advanced to F2 by controlled full-sib matings. Tests of weevil antibiosis of grain were conducted under controlled temperature and relative humidity. Fifty-gram samples of each hybrid and line were infested with 32 unsexed weevils for 10 days. F1 progeny were counted at 2-day intervals until all progeny had emerged. Some hybrids had detrimental effects to weevil-biology (antibiosis), as hybrids differed significantly for adult mortality (0 to 89%), progeny emergence (1 to 188 weevils), development period (29 to 44 days) and relative index of susceptibility (0.3 to 11.7). Variation for index of susceptibility (antibiosis) among hybrids was more in F1 than F2 generation. Additive, non-additive, and maternal effects were significant in determining weevil resistance for F1 seed and F2 grain. Variance of GCA effects for lines used as females was larger than that for lines used as males, suggesting that breeders developing weevil resistant hybrids hould place greatest emphasis on choice of the female parent. Results indicate that it is essential to evaluate weevil resistance of F2 grain, because we generally found no relationship between performance in F1 and F2, and because it is weevil resistance in F2 that is of practical significance to farmers and grain merchants.